Certified GKH Gardening Expert
It's hard to say without knowing what kind of plant. Some are easier than others to tell whether flower buds or leaves during early formation.
Start with this article: https://www.gardeningknowhow.com/garden-how-to/info/plant-bud-information.htm
In order to encourage flower formation, don't use a high nitrogen fertilizer, which stimulates vegetative growth, sometimes at the expense of reduced flower formation.